This invention relates to machine tools of the kind having a working space in which powered operations are carried out by a power-driven movable element on workpieces, and having means designed to minimise the risk of injury to the operator by preventing his hands being present in the working space during the periods of time when the powered operations are in progress.
Such protective means have taken various forms. For instance, there may be two machine control buttons spaced apart so that they cannot both be reached by the same hand of the operator, and both of which must be pressed by the operator to initiate a working operation and kept pressed throughout the operation, so that the operator's two hands must both be occupied well clear of the working space throughout the working operation. Such protective means have the disadvantage that the operator is not free until after the completion of each operation to perform other tasks such as getting the next workpiece ready for placing in the working space.
In other protective means a movable guard is provided for the working space, which is actuated automatically by the machine so that it is moved to close off the working space before the working operation begins. Such guards often are arranged to move in such a way as to push the operator's hand or hands out of the working space. Such guards are not wholly reliable and occasionally an operator's hand may become trapped and accidental injury may ensue. Further, as such guards must be actuated with sufficient force to push the operator's hands away, the closure of the guard itself may sometimes cause an injury. Also, as their operation is closely tied in with the working operations of the machine, they are not amenable to independent actuation by the operator.